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The Dow Jones Industrials gets so much attention among both investors and the general public because it's the market measure that's easiest to understand. Not only is the math in calculating the average simple, but all the companies in the Dow are also well-known household names that play a role in just about every American's daily life, and investors rarely have to worry about major problems with Dow component companies.

Yesterday, we looked at some of the Dow stocks that are true leaders in their respective fields. But many Dow stocks aren't at the top of their industries and instead are striving to become the kings of the hill. Just because a company isn't the biggest doesn't mean it's not as good an investment, so let's take a closer look at these up-and-coming Dow stocks to see whether they look promising.

American Express : 1-year return 26.8%, 5-year average annual return 9% American Express certainly has a strong marketing presence, but as a card network, it's a distant No. 3 to Visa and MasterCard. Although the company is more widely diversified than its card-network rivals, with a variety of travel-related and other financial services, AmEx still identifies many of its biggest growth opportunities as card-related.

AmEx made a huge move toward broadening its base and becoming more of an industry leader when it released its new Bluebird prepaid card last October. Given AmEx's reputation for aiming at affluent customers, Bluebird opens up a brand-new demographic for the company, as the card targets customers who don't even have bank checking accounts and other traditional banking services. With reasonable fees, the AmEx offering could give the company the chance it needs to connect with new customers and grow its business substantially.

Travelers : 1-year return 28.5%, 5-year average annual return 10.8% Property and casualty insurers across the industry have labored under the shadow of AIG for years. Even after the near-failure and government bailout of the insurance giant, AIG still has huge amounts of revenue and a bigger market capitalization than Travelers. Still, Travelers has plenty of business, and without the stigma of taking TARP money, the company has a marketable advantage over AIG.

Of course, the ups and downs of the P&C insurance industry will continue to play a big role. Travelers took hits from hurricanes Irene and Sandy, but the stock has nevertheless held up extremely well. Despite near-term catastrophe losses, the long-term impact of higher rates could end up being a net positive for Travelers.

Merck : 1-year return 17.2%, 5-year average annual return (2.2%) Merck is a drug giant in its own right, but it's still a bit smaller than rival Pfizer. Both drug companies have labored under the same difficulties lately, though, facing big patent cliffs that have forced them to develop new pipelines of promising drug candidates. Moreover, if Pfizer moves ahead with a decision to split itself into component parts, then Merck may inherit the leadership role by default.

In 2013, Merck is hoping to see some successes from multiple prospects that include treatments for osteoporosis, ovarian cancer, and human papillomavirus. Although the company had to pull the plug on its Tredaptive cholesterol drug, rising optimism about Merck's potential could drive investors into the stock even as its rivals choose to break themselves apart.

Will these companies catch up?These four stocks have generally put up pretty strong performances recently, suggesting that companies with something to prove do their best to push ahead and take over the reins from their rivals. Even though these companies don't yet lead their industries, they have plenty of strong qualities that bode well for their respective futures in the years to come.

The right time to buy tomorrow's leaders is before they become leaders. To learn how to find those stocks, please accept this invitation to take a personal tour with Motley Fool co-founder David Gardner of his Supernova service. David is renowned for making picks with great insight into the futures of their respective industries, so don't wait -- click here to get instant access to your tour today.